Succinate (butanedioic acid) is a four carbon dicarboxylic acid that plays a key role in the citric acid cycle. Succinate was recently listed by the US Department of Energy at the top of its list of value added chemicals from biomass. Succinate is a precursor for a number of compounds, including tetrahydrofuran, 1,4-butanediol, and γ-butyrolactone. Succinate has a wide variety of potential applications including use in liquid antigels, heat transfer fluids, the solvents gamma butyrolactone (GBL) and dimethyl isosorbide, pigments, the polyesters poly-butylene succinate (PBS) and PEIT, synthesis intermediates and plasticizers.
Succinate has traditionally been derived from maleic anhydride, which is produced by oxidation of butane. In recent years, there have been several attempts to move away from these traditional production methods to biological production methods. Biological production provides several advantages over derivation from petrochemical sources, including increased efficiency and cost effectiveness and decreased environmental impact.
Previously-developed biological succinate production methods have primarily utilized bacterial fermentation hosts. Although several bacterial species have been used successfully to produce succinate, bacteria present certain drawbacks for large-scale organic acid production. As organic acids are produced, the fermentation medium becomes increasingly acidic. These lower pH conditions result in lower costs for organic acid production, because the resultant product is partially or wholly in the acid form. However, most bacteria do not perform well in strongly acidic environments, and therefore either die or begin producing so slowly that they become economically unviable. To prevent this, it becomes necessary to buffer the medium to maintain a higher pH. However, this makes recovery of the organic acid product more difficult and expensive.